Process for solvent dewaxing oils



Patented Feb. 1, 1938 UNITED STATES PATENT OFFICE PROCESS FOR SOLVENT DEWAXING OILS Delaware No Drawing. Application April 8, 1935, Serial No. 15,290. In the Netherlands April 25, 1934 10 Claims.

This invention relates to a process for separating waxy substances from mineral oils, such as petroleum oils, tar oils, shale oils, brown coal distillation oils, and the like. More particularly, this invention is concerned with the use of a new solvent or diluent mixture for aiding the separation of waxy substances from the oil.

Mineral oils naturally contain varying amounts of high melting hydrocarbons hereinafter, for convenience, designated as Waxes which at normal or at elevated temperatures are liquid or dissolved in the liquid hydrocarbons, but which solidify into amorphous or into crystalline form at lower temperatures. When these wax-bearing oils are used at such lower temperatures the waxes may resist or obstruct the desired flow of the oil. Moreover, when the wax content is too low to impede materially the flow of oil, it may, nevertheless, cause an undesirable cloudiness. It is, therefore, often necessary to effect the removal of at least a portion of these waxy constituents. The removal of wax from oil, and more particularly the removal of mineral Wax from mineral oil has in the past been accomplished by the dilution of the wax-bearing oil with a suitable diluent or diluent mixture, followed by chilling the solution to precipitate the wax, and the separation of the precipitated wax by some suitable means, such as filter pressing. The function of the diluent was to reduce the viscosity of the chilled mixture, whereby theseparation of the wax was facilitated.

It has also been proposed to aid the separation of the solid Wax by using diluents possessing selective solvent properties, i. e. having a high solvent power for liquid hydrocarbons, but none or only a slight solvent power for solidified wax. Acetone, ethyl alcohol, naphthas, etc., and mixtures of acetone and benzol have been suggested as diluents for this purpose.

It has, in the present invention, been found that particularly good results are obtained by using as a dewaxing diluent or solvent, a mixture of one or more partially hydrogenated naphthalenes which may or may not have aliphatic side chains, such as tetrahydronaphthalene and one or more liquids having selective solvent properties but low solubility for oil, such as lower sym- 1 tone, ethyl methyl ketone, diacetone alcohol, methyl formate, methyl acetate, ethyl acetate, acetic acid, butyric acid, lactic acid, acetic anhydride, methyl carbonate, ethyl formate, butyl alcohol, quinoline, iso-quinoline, pyrrole, furfural, etc. The aliphatic solvents are characterized by having not more than five carbon atoms in the molecule. Although I have enumerated a number of solvents which may be used with hydrogenated naphthalene in a dewaxing solvent mixture, my invention is not limited thereto, but may be employed in connection with other analogous solvents.

These constituents may be mixed inany desired proportion, depending upon the amount of Wax to be separated, upon the dilution ratio and upon the separation temperature. It is essentialthat the mixture have a high solvent power for the liquid hydrocarbons and a low solvent power for the solid hydrocarbons at the temperature at which the separation of the solid from the liquid hydrocarbons occurs. The low solubility selective solvents, of which the ketones constitute the preferred group, are effective for separating solid and liquid oil components, due

a to the difference in solubility of such oil 'components in these solvents, but this action is limited by their low solubility in the oil at the low or moderate temperatures of the deWaxing operation. The partially hydrogenated naphthalene increases the solubility of oily components. The optimum condition is that at the filtering temperature the oil is just completely dissolved, an eflicient precipitation of the wax without occlusion of oil being thus obtained. Under certain conditions the partially hydrogenated naphthalene has the further effectof reducing the viscosity of the oil to aid in the separation of the liquid and solid phases. With these desiderata and the function of the components of my mixture in View, the proper ratio may be readily determined empirically in each particular case. It is often preferable to use a eutectic mixcan be readily determined in any particular instance by those skilled in the art. By the term efiective quantity as used in the claims, I mean the quantity of solvent mixture which will maintain sufiicient oil in solution .to produce its substantial separation from the Wax which is precipitated, and which will produce an oil-solvent mixture of the desired viscosity.

In carrying out my invention, a wax-bearing oil may be mixed with my. solvent mixture at normal or at elevated temperature,-chilled to precipitate the wax, and separated from the precipitated wax, which may be either crystalline or amorphous, by any known means, such as filter pressing, centrifuging, or cold settling. The separation temperature largely determinesthe melting point and the quantity of the wax which is separated. The dewaxing may be conductedeither as a continuous or as a batch process. It is sometimes desirableto precipitate the wax in several stages, thereby producing a number of waxes of difierent melting points. According to this method, thefirs't precipitation and separation is carried out at a temperature which is ,sufilciently high. to, solidify only the highest melting components, and the filtrate is chilled to effect further separation of wax at one or more stages at successively lower temperatures. The amount of the dewaxing mixture in the, oil may, moreover, be varied at each stage so as to be present in the correct quantity to dissolve substantially all of the oil at .the particulartemperature'while not causing the dissolution of substantial amounts of the solid wax. Thus, it is often necessary to below its boiling point add more dewaxing stage.

It is generally desirable, but not essential, to produce a homogeneous oil-wax-solvent system solvent at each successive prior to the precipitation step. To achieve this The solvent mixture may be recovered {fromthe oil and from the wax by evaporation or by vacuum distillation and reused. A particular advantage ofthe process according to this invention is that evaporation losses during the dewaxing operation and in the-recovery of the dewaxing solvents are smaller for the present method than for methods employing mixtures used heretofore.

An exampleof the use of a diluent mixture for dewaxing is as follows, it being understood that my invention is not limited to the particular substances, ratios, quantities and operating conditions appearing therein. I

One part of a lubricating oil having a pourpoint of 37 C. was mixed with three parts of a mixture of equal quantities of acetone and tetrahydronaphthalene, chilled to 20 C. and filtered. The pour-point of the filtrate was -13 C.

It will also be understood that in some cases a three-component mixture containing partially hydrogenated naphthalene, a selective solvent of low solvent power, and a third substance of intermediate solvent powerQsuch as an ether, may be used. The additional component should, preferably, have some selective solvent properties.

Moreover, it is not necessary to mix all of the components of the solvent mixture before dissolving them in the oil. Thus, the partially hydrogenated naphthalene may be added first, either alone or with small amounts of the second component, followed by the addition of the requisite amount of the second component.

I claim as my invention:

1. A process for dewaxing oil by mixing the oil with a liquid dewaxing agent having a high solvent power for the oily components of the waxbearing oil but low solubility for its waxy components, chilling the resulting mixture to precipitate waxy components and separating the precipitated material from the oil-containing solution, characterized by the use as the dewaxin agent of a mixture comprising a partially hydrogenated naphthalene and a selective solvent having a low solvent power for oil.

2. A process for dewaxing oil by mixing the oil with a liquid dewaxing agent having a high solvent power for the oily components of thewaxbearing oil but low solubility for its waxy-components, chilling the resulting mixtureto precipitate waxy components and separating the precipitated material from the oil-containing solution, characterized by the use asthe dewaxing agent of a mixture comprising a partially hydrogenated naphthalene and an aliphatic ketone having not more than five carbon atoms in the molecule.

3. A process for dewaxingoil by mixing the oil with a liquid dewaxing agent having a high solvent. power for the oily components of the waxbearing oil but low solubility for its waxy components, chilling the resulting mixture to precipitate waxy components andseparating the precipitated material from the oil-containing solution, characterized by the, use as the dewaxing agent of a mixture comprising 'tetrahydronaphthalene-and an aliphatic ketone having not more than five carbon atoms in the molecule. 7

4. A process for dewaxing oil by mixing the oil with a liquid dewaxing agent having a high solvent power for the oily components of the waxbearing oil but low solubility for its waxy components, chilling the resulting mixture to precipitate waxy components, and separating the precipitated material from the oil-containing solution,

characterized by the use as the dewaxing agent ofJa mixture consisting of 'tetrahydronaphthalene and acetone. h

5. A process of dewaxing mineral lubricating oils comprising the steps of mixing a wax-bearing oil with an efiective quantity of 7 an aliphatic ketonehaving not more than five carbon atoms in the molecule, precipitating the wax from-the resulting mixture in the presence of a quantity of partially hydrogenated naphthalene, saidquantity being sufiicient to prevent the separation of substantial amounts of oil from the oil-solvent mixture during the precipitation, and mechanically removing the precipitated oil from the solu- 7. A process of dewaxing mineral lubricating oils comprising the steps of mixing a wax-bearing oil with effective quantities of an aliphatic ketone having not more than five carbon atoms in the molecule, and a partially hydrogenated naphthalene, said quantities being sufiicient to prevent the separation of substantial amounts of oil with the solidified wax when the oil-wax-solvents mixture is chilled, and chilling the resulting mixture to solidify the wax.

8. A process of dewaxing mineral lubricating oils comprising the steps of mixing a wax-bearing oil with an eifective quantity of the eutectic mixture of an aliphatic ketone having not more than five carbon atoms in the molecule, and a partially hydrogenated naphthalene, said quantity being sufficient to prevent the separation of substantial amounts of oil with the solidified wax when the oil-wax-solvents mixture is chilled, and chilling the resulting mixture to solidify wax.

9. A process for dewaxing mineral lubricating oil comprising the steps of mixing a wax-bearing oil with an efl'ective quantity of an aliphatic ester having not more than five carbon atoms in the molecule, precipitating the wax from the resulting mixture in the presence of a quantity of partially hydrogenated naphthalene, said quantity being sufficient to prevent the separation of substantial amounts of oil from the oil-solvent mixture during the precipitation, and mechanically removing the precipitated oil from the solution.

10. A process for dewaxing mineral lubricating oil comprising the steps of mixing a wax-bearing oil with an effective quantity of an aliphatic alcohol having not more than five carbon atoms in the molecule, precipitating the wax from the resulting mixture in the presence of a quantity of partially hydrogenated naphthalene, said quantity being sufficient to prevent the separation of substantial amounts of oil from the oil-solvent mixture during the precipitation, and mechanically removing the precipitated oil from the solution.

HENDRIKUS VAN DER WAERDEN. 

